1. Field of the Invention
The invention relates generally to a chemical methodology for protecting sensors from biofouling, especially those in contact with fresh water, seawater, wastewater, effluent, or high humidity environments, and in particular the invention relates to antifouling biocidal compounds and/or mixtures that are active at parts-per-million (ppm) and/or parts-per-billion (ppb) concentrations.
2. Related Art
The occurrence of biofouling is a common problem for surfaces in contact with fresh water, seawater, wastewater, effluent, or high humidity environments. Although only considered a nuisance in many instances, biofouling in aquatic sensors is detrimental to the life of the sensor and the quality of data collected by such sensors. Previously, non-mechanical antifouling methodologies have been developed for the treatment of heat exchangers, platforms, pools, ponds, ships, submarines, and even industrial plants. However, to date, no one has developed a non-mechanical, non-electrical antifouling methodology for sensors. Reference U.S. Pat. No. 5,889,209 for a mechanical antifouling apparatus for aquatic sensors.
Historically, sensors have been employed to detect the presence of analytes in biologically active media, such as oceans, lakes, streams, rivers, wastewater treatment facilities, and industrial effluent. The problem that has plagued both the manufacturers and users of the sensors is that within hours of being submerged within a biologically active media, all surfaces develop a bacterial film. This film subsequently acts as a substrate for algae growth. The net effect of the formation of bacteria and algae is sensor drift, which is an undesirable trait for long-term monitoring.
Prior non-mechanical, non-electrical, chemical-based antifouling methodologies have consisted of leachable or photocatalytic biocides (metal oxides), as described in U.S. Pat. No. 5,518,992, embedded within an inert binder, polymer, or xe2x80x9cself-polishing copolymerxe2x80x9d paints, as described in U.S. Pat. No. 5,717,007. U.S. Pat. No. 5,776,856 discusses the use of water-soluble matrices for water-insoluble, agrochemically active chemicals for crop treatment. U.S. Pat. Nos. 4,818,797, 6,017,561 and 5,116,407 discuss the use of quaternary ammonium compounds and amines that behave as binders and marine biocides, and work in combination with acid functional polymers. The acid groups of these polymers are blocked by the ammonium compound or monoamine group, which form an organic-solvent-soluble salt of the polymer.
Recently, U.S. Pat. No. 5,849,311 disclosed non-leaching metal based biocidal materials as well as methods of manufacture and use of such materials. Finally, U.S. Pat. Nos. 5,902,820, 5,981,561, 5,981,582, 5,998,391, and 6,004,947 all discuss methods for using synergistic admixtures of biocidal compounds to treat surfaces.
Unfortunately, the high biocide concentration levels associated with the aforementioned approaches causes the biocides to interfere with many sensors, thus making such technologies inapplicable to sensor protection. This is especially true for optical sensors, or xe2x80x9coptrodesxe2x80x9d,in which chemical reactions between a sensor and some biocides can cause sensor failure. A secondary concern is the leaching of the biocide from a containing matrix, which has also been shown to significantly affect the performance of optrodes.
Some have sought to rectify such shortcomings through software-oriented approaches. For example, some in the prior art periodically recalibrate optrode or other sensor inputs to ensure accurate readings. Others in the prior art use software to control application of periodic, relatively high energy electricity to a sensor, thereby retarding biofouling.
The present invention provides a non-electrical, non-mechanical, and non-software oriented methodology for protecting sensors, with specific applicability to retarding or eliminating optrode biofouling. The use of optrodes for the determination of many different analytes in a number of environments is well documented. One commonality between all optrodes is that they exhibit phenomena such as temperature sensitivities, cross-sensitivities to other analytes, pH dependencies, and support/solvent interactions. Support/solvent interactions are interactions that develop as a result of embedding luminescent probes in a support matrix.